Carrier-signaling system



E. I. GREEN CARRIER SIGNALING sYsTfil Original Filed Deg. 30, 1925 AME w Aug. 20, 1929.

ATTORNEY Patented Aug. 20, 1929.

. UNITED STATES PATENT: orrlca.

ESTILL-I. GREEN, 0] EAST ORANGE, NEW JERSEY,

ASSIGNOB TO AMERICAN TELE mom: AND rannenarn oomramr, a ,coaroaariox or raw-roan.

I cmxmsrcminvo srsrm Application filed December 80, 1825,8eria1 No. 78,454. Renewed November 11,

' This invention relates to carrier signaling systems, and particularly to amethod and means for substantiall equalizing the transmission equivalents of a plurality of chan, nels difl'erin in frequency transmitted over or throught e same transmitting medium.

In carrier systems having several repeaters, it has been found necessary to e ualize the volumes of the various channels efore amplifying them at each repeater in order to keep the highest frequency channel (which has the greatest attenuation) above the noise level and at the same time to'kee the lowest frequency channel (which has t e least at tenuation)- below the overload point of the repeaters. This equalization of the various channels is ordinarily carried out by means of networks which reduce all channels to the same level at each repeater point. This practice of reducing the volumes of all the channels to substantially the same level, which in practice is the'level of the highest frequency channel, is highly inefficient because of the waste of energy of the lower frequency channels.

' means for equalizing the transmisson equivalents of a plurality of channels of different frequencies transmitted over or through a common transmitting medium, which method consists in inverting the channel frequencies in alternate repeater sections. Suchmethod has distinct advantages over the method here tofore employed in thatthe present method equalizes the channels with respect to. their frequency of transmissiomwhich is the real difference between. the channels, rather than with respect to attenuation, which is only a characteristic of the frequency. The equalization of the channels with respect to frequency effectively provides equalization with respect to all the factors-whichzare a function of frequency, such as gain, noise, crosstalk, attenuation Variations, and other similar functions. v

This invention will be clearly understood from the following description when read in connection with the attached drawing, show ing symbolically a, form of embodiment of the invention.

In the drawing, the terminalstat-ion A comprises a plurality-of branch -circuits each This invention resides in a method and.

intended for the handling of one of the' channels of transmission. Thus circuit 1 is intended to handle one of the channels of transmission, which channel represents preferably one ofthe side bands the modulation of a carrier fr uency by a signal frequency, as, for examp e, the band of speech. frequencies, and, in like manner, circuits 2, 3 and 4 are each adapted to handle otherchannels of transmission. All of the branch circuits, which, taken together make up the terminal stationfare connected with a common transmitting medium, such as the wire circuit L The transmission line L is made up of a pluralit of line sections, some of which, designated X, Y and Z, are shown. means of repeaters. Thus, re eater No.1 is connected between sections and Y, and repeater No. 2 between Y and tlon Z may be connected with another repeater interposed between it and a succeeding section of the line L,, or it may be connected' with a terminal station substantially similarto' station A. In any event, the distant ,end of the line L would be terminated by a plurality of branch circuits, such as is shown in station A.

At station A the transmitters 5 to 8, inclusive, represent symbolically any means for impressing'a modulating current upon the input sides of a plurality of modulating devices 9 to 12, inclusive, which, respectively, are connected with the circuits 1' to 4, inclusive. While these modulating devicesmaybe of any well-known type, a preferable form is a vacuum tube arrangement characterized by the suppression of the carrier frequency, which is disclosed in the patent to Carson, No; 1,449,382, dated March 27, 1923. .Also connected with the input sides of thenrodulators 9 to 12, inclusive, are the. sources of carrier fre uency 13 to 16, respectively, each .of whic is adapted to Z. The secproduced by I These sections are connected b a produce a frequency that differs from the others. A plurality of filters, to 20, inclusive, put circuits of the modulators 9 to 12, respectively. The filters 17 to 20, inclusive, are in turn connected with the line While the circuits 1 to 4 represent only the designated 17 transmitting branches for the channels of transmission, it is to be understood, of course, that receiving branches of wellare connected with the outknown types would ordinarily be employed at the terminal station A toreceive at that terminal station the currents of each channel which are transmitted from the distant end .-by circuits such asar'e shown in the drawing.

Repeater No. 1 comprises two oscillators 21-and 22 the former being connected across the line 151 at the input side of the modu lator 23. A filter 24 is connected across the outputside of the'modulator 23. The oscillator 22 is comiected across the input side of the modulator 25, across the output side of which is a filter 26 which is also connected with the input side of an amplifier 27. The out ut side of this amplifier is connected wit the line section Y, which in turn is connected with the repeater No. 2, having parts similar to those shown at repeater No. 1 and which bear the same designating numerals primed. The manner in which this circuit operates in order to attain the objects of the invention is as-follows:

Let it be assumed that the oscillator 13 of the branch circuit 1 is producing such a. car'- rier frequency that when modulated by the signal frequency roduced by 5, it will produce such side bands that. one of them, namely, the one transmitted by the filter 17, will have the ran e of '6 to 10 kilocycles. In like manner, t e circuit 2 will have a source of oscillations of such frequency that upon by the selected side band will have the range of 11 to la kilocycles, channel 3 a selected range of 16 to 20kiloc cles, channel 4, 21 to 25 kilocycles, and ot er channels which may be connected with the line I}, may have other frgquencies ranging up to kilocycles. of the frequencies represented by the various channels would, when impressed upon the line L,, be transmitted thereover, At repeater No. 1 the frequencies present in the channels would be operated of the channels would be inverted, amplified and transmitted over the line section Y to repeater No. 2, where the frequencies im-, pressed on that re ater would again be inverted and. ampli ed and transmitted over sectlon Z. B this inversion of the frequencies, the c annels of higher frequencies which were attenuatedmost in the transmis- S1011 over line section X would be translated to lower frequencies so as to'be least attenuated in transmission. oversection Y,

and similarl the channel of lower frequencies that ha the least attenuation in transmission over section X would be translated to higher frequencies by repeater No. 1,

which would have the greater attenuation in transmission over section ,Y. In this manner the uivalents of the various channels are maintained substantially equal. The manner in which each of the. repeaters "operate to produce this result will be clear the apparatus. present at the re peater m such manner that the frequencies by describing what happens at repeater No. 1. The assumed range of fre uencies extending from 6 to 50 -kilocyc es will I be beaten in the modulator 23 with a source of of from 6 to 50 kilocycles. .'Thus channel.

1, which, at terminal station A has a range of 6 to 10 kilocycles, becomes, afterpasslng through the filter 24, to 94 kilocycles,

and the channel at station A, which has the highest frequency, namely 46 to 50 kilocycles, passes through the filter 24 as 50 to 54 kilocycles. In other words, the range at terminal station A of 6 to 50 *kilocycles becomes at the filter 24, 50 to 94 kilocycles.

These frequencies, which are transmitted by the said filter, are then beaten with oscillation'sfrom the source 22 which has a fre- 9 3 f4 which is equal fa (f1 .f2)1 where f, is the frequency of'the oscillator 21, f, the lowest frequency present in all of the channels on the line L,, and f, the highest frequency present. In the present case, f,+f,=56, so that the frequency f, of the oscillator 22 must be 44 kilocycles.- Thus the frequencies transmitted through the filter 24, which range from 50 to 94 kilocycles, will be beaten with 44 kilocycles and produce difference frequencies ranging-from 6 to 50 kilocycles, which difference frequencies will be transmitted by the filter 26 and amplified by 27. It has been pointed out that the frequency 94 transmitted through the filter 24 corresponds to the frequency 60f channel 1 at station A, and the frequency 50 corresponds to the. frequency 50 of channel 28 at station A. The frequencies transmitted' through 24, when beaten with the oscillations of '44 kilocycles,'produce sum and differencefrequencies, the difference frequencies ranging from 6 to 50 kilocycles, The

frequencies in the line section X will be thus 1'50 completely inverted because the frequency of 50vk1locycles at the filter 26 corresponds to 6 kilocycles at terminal A, and 6 kilocycles at the filter 26 corresponds to 50 kilocycles at station A.- It will accordingly be seen that the higher frequencies at station A, which were transmitted over section X of the line and attenuated to the highest degree, have been so reduced in frequency-by the beating operations at repeater No. 1 that. they will notbe subjected to such a high degree of attenuation after being amplified by the amplifier 27 and transmitted over section Y of the line L, to the repeater No. 2.-

The lower frequencies transmitted over section X of the line, which were least atten-.

uated, are translated at repeater No. 1 to higher frequencies which, .when amplified by 27 and transmitted over the line section Y,

- that as the result of such frequency translation at the repeaters connected with the line- L,, the equivalents of a plurality of chan- ,nels are maintained substantially equal.

These frequencies comprising the various.

channels will be received at a terminal station connected with the distant end'of the line L and translated, so that the signals impressed upon the transmitters 5 to 8, inclusive, at terminal A will be detected. While the arrangement shown in the draw- I ing represents only a one-way system, it is to be understood, of course, that the system may be rendered operative in both directions by methods well known to those skilled in the art.

By means ofthe system of double beating disclosed herein, it is possible to effect the inversion of a plurality of frequencies present in a plurality of channels of transmission without dividing the channels into groups and translating each of these groups separately, which method is disclosed in the copending application of Green, Serial No. 78,455, filed December 30, 1925, Patent No. 1,677,966, granted July 24, 1928.

While this invention has been disclosed as embodied in a particular form, it is capable of embodiment in other and different forms without departing from the spirit and frequency, selecting the difference frequencies resulting from said beating operation, beating the said difference frequencies with a beating frequency equal to the difference between the said first beating frequency and the sum of the lowest and the highest freuency in all of the said channels, selecting t e difference frequencies from the said second beating operation, and transmitting the selected frequencies.

2. The method of sion equivalents of a plurality of carrier channels which consists in beating a pluralthe same channel equalizing the transmisity of frequencies with oscillations whose frequency is at least twice as great asfthe highest frequency in'all of the said channels,

and selecting the difference frequencies in each channel, beating the selected frequencies with a frequency equal to the difference between the first beating frequency and the sum of the lowest and the highest frequencies in all channels, selecting the difference frequencies of the latter beating operation,

amplifying and transmitting the latter selected frequencies.

3. In a carrier'signaling system, the combination with a transmission line of a repeater between sections thereof, a source of current representing a plurality of channels of transmission connected with the said line the said repeater comprising a source of beating oscillations whose frequency is at least twice that of the maximum frequency of all channels, a filter to ass the difference frequencies from the said eating operation, a second source of beating oscillations whose frequency equals the difference between the frequency of the said first source and the sum of the lowest and highest frequencies in all channels, and a filter to select the difference frequencies from the said second beating operation.

4. In a carrier signaling system, the combination with a transmission line of a repeater between sections thereof, a source of current representing a plurality of channels of transmission connected with the said line, the said repeater comprising a source of beating oscillations whose frequency is at least twice that of the maximum frequency of all channels, a filter to pass the differ ence frequencies from the said beating opera. tion, a second source of beating oscillations whose frequency equals the difference between the frequency of the said first source and the sum of the lowest and highest frequencies in all channels, a filter to select the difference frequencies from the said second beating operation, and an amplifier to amplify the selected frequencies. Y

5. The method of equalizing the transmission equivalents of a plurality of carrier channels, which consists in transmitting the currents representing a plurality of channels of different frequencies, beating all ofthe said frequencies with a beating frequency of predetermined magnitude, selecting one of the bands of fre uencies resulting from the said heating -0 each channel,

beating the selec ted bands with another heating frequency and selecting that band of each channel that contains the frequenciesthat are-an inversion of the frequencies of prior to the first beating operation.

6. In a multi-channel high frequency signaling system, the method of equalizing the over-all line attenuation for several simila rly directed vchannels, which consists in beating the frequencies of each channel with the same beating frequency, selecting one of the bands of each channel resulting from 5 such beating and heating it with another beating frequency, and selectingone of the bands of each channel resulting from thesecond beating operation, the said heating frequencies being so chosen that the -.fre-" 10 quencies of the r st selected band of each channel when beaten with the secondbeating frequenc shall produce aband of that chann'el'which is the inverse of the frequencies of that same channel prior to the first/beat 1 ing operation.

In testimony whereof, I have signedmy name to this specification this 29th day of December, 1925.v 1

ESTILL 'I. GREEN. 

